Predictability of Zimbabwe summer rainfall

✍ Scribed by Makarau, Amos; Jury, Mark R.

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 416 KB
• Volume: 17
• Category: Article
• ISSN: 0899-8418
• DOI: 10.1002/(sici)1097-0088(19971115)17:13<1421::aid-joc202>3.0.co;2-z

✦ Synopsis

Predictors of Zimbabwe summer rainfall are investigated with a view to improved long-range forecasts. Teleconnectivity is assessed in respect of sea-surface temperatures, the Southern Oscillation index, the Quasi-biennial Oscillation (QBO), outgoing longwave radiation (OLR) and wind. Spectral analyses of historical rainfall gives an indication of cycles in the range 2Á3, 18 and 3Á8 years, possibly associated with the QBO, the luni-solar tide and the El Nin Äo±Southern Oscillation (ENSO), respectively. Pair-wise correlations are found between Zimbabwe summer rainfall and SST in the central Indian Ocean (r À0Á5) in austral spring. Below normal OLR values in September over southern Africa corresponds with good rains in the following summer. Rainfall±upper-wind correlations are optimum (r À0Á7) over the equatorial Atlantic in spring. Comparatively weak correlation with the QBO may also re¯ect biennial adjustment of monsoon and global ENSO teleconnections. Additional predictor variables are utilized and multivariate models are formulated for early and late summer rainfall and maize yield in Zimbabwe. The models use three to ®ve predictors, are trained over a 22-year period and perform well in jack-knife skill tests. Summer rainfall forecasts with one season lead times are viable and could ameliorate hardship caused by drought.